We have discovered that a purified cell adhesion molecule, the 8D9-antigen can serve as a potent substrate for neurite growth in vitro. The 8D9-antigen is similar or identical to NILE, L1 and Ng- CAM. Using a novel in vitro assay it is now possible to further characterize the biochemical properties of the 8D9-antigen as well as begin a rational search for the 8D9-receptor. It has been demonstrated that this class of cell adhesion molecule is present during development of the nervous system but disappears in many parts of the mature nervous system. It is also known that it reappears in the regenerating peripheral nervous system. This suggests that the 8D9-antigen may serve a permissive, if not essential, role in regeneration of axon pathways. Therefore, we propose to investigate the use of this molecule as a substrate for promoting regeneration in the peripheral and central nervous systems.